In the past, alternating magnetic fields from electromagnets have typically provided an alternating potential which is developed at the electrodes to facilitate signal amplification and processing, and to prevent electrode polarization, a condition which introduces serious measurement error. Alternating magnetic fields, however, introduce several considerations, including a substantial electrical power requirement, the generation of electrical noise, and the requirement of complicated electrical circuits. This invention alleviates such considerations by enabling accurate measurement to be made using permanent magnets and a highly efficient magnetic circuit. The highly efficient magnetic circuit may also be used with flow sensors incorporating electromagnets which will then develop larger potentials at their electrodes and diminish the difficulties associated with those sensors.
Conventional magnetic flow sensors are available in both the probe and the full bore configurations. The invention described herein applies to both forms and enjoys the advantages of relatively high induced voltage and low noise, thereby reducing the cost and complexity of the supporting electronics, and relatively low power consumption, a particular advantage for portable instruments.
It is an object of the invention to provide a magnetic flow sensor using permanent magnets which are periodically mechanically repositioned to alternate the magnetic field polarity engaging the conductive fluid, thereby producing an alternating potential at the electrodes.
It is another object of the invention to provide a magnetic flow sensor with a magnetic circuit which substantially increases the potential developed at the electrodes.